I saw on fb someone saying it can take up to 6 months to get your passport back and I panicked!
It can potentially take that long... their service standards time for processing ILR postal applications is 6 months, though it does depend on how busy they are at the time you apply. I think someone here applied by post a few months ago and it was a fair bit less than 6 months.
If you apply in person, you get the decision the same day (and all your documents back) and then your BRP card is sent in the mail within 10 days, though most people seem to get it in about 4 days.
It does cost an extra £610 to apply in person though, on top of the £2,389 application fee, and the appointments are released 42 days in advance... they can book up quickly, so you'll want to plan ahead, check availability and give yourself plenty of time to book it
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One thing to be aware of though, is that if you have a non-straightforward application (any previous refused visas or entries to the UK, or any criminal convictions), you can't apply in person, because they will need to spend more time looking at the application, which means they can't make a same-day decision.
See here for more information about applying in person:
https://www.gov.uk/ukvi-premium-service-centresAnd the ILR application form and guidance is here:
https://www.gov.uk/government/publications/application-to-settle-in-the-uk-form-setm